Fluid servo apparatus



April 21, 1953 H. E. KARIG FLUID SERVO APPARATUS Filed Jan. 2'7, 1949 V 6 m M u o 7 0 m L H l 15 I! A A i M G I A u k R m a wy "(A B In Patented Apr. 21, 1953 Lil.

V UNITED STATES PATENT OFFICE FLUIVD sERvo immune Horace E. Karig, Pasadena, Calif; Application January 27, 1949, Serial No. 73,211

, 2 Claims. (oi. 12138.) (Granted under Title 35, U. s. Code (1952),

- sec. 266) that is to say, to an apparatus in which the flow of fluid thru a system of conduits is employed to transmit and preferablyalso amplify in power the movement of a control member. 7

-It is an object of this invention to provide a'fluid servo system, the output signal from which will be a combined function representing both the inputsignal and the rate of change of the inputsignal. V e V Itis another object of this invention to provide a push-pull fluid servo system, in which a pair of substantially identical control devices are'so interlinked and are so fed with suitable fluid pressure signals that their output acts in a common sense or direetion to transmit to an output member a signal which varies both with the-input signal and with the rate of change of the input s na a A -.It isa further object of this invention to provide in a fluid servo system a valve member and a servo mechanism controlled thereby, and linkage means between the two, so that the servo mechanism may be caused to occupy a position corresponding to that of a v movable member forming a portion of the valve.

in isanother object of the instant invention to provide a fluid servo or control system in which the'output signal is responsive to both the input signal and'the rate'of change in the input signal, and means in thesystem for selectively attenuatingihigher frequency responses which result from high frequency rate responses in, the signal, thereby rendering the. system more stable.

-Other-Objects and many of the attendant advantages of the instant invention will be readily appreciated as the same becomes better under.- stoodby reference tothe following description. j .O;n'e of the importantelements of the system of the instant invention is an apparatus for deriving a force proportional simultaneously to the pressure of a fluid (which pressure represents an input signal) and also to the. rate ofchange of this pressure. This apparatus comprisesapair of opposed, expansible chambers separated by suitable diaphragm'means, so that as'one chamhas a restriction (preferably adjustable) therein, so that upon a sudden change in input pressure,- the fluid pressure in the second of the two chambers does not change as rapidly as that inthe first. The first chamber, having direct communication with the input conduit, is thus sensitive to rate of change of input pressure, while the second chamber, which is fed only thru the restrictedconduit, is responsive to the fundamental signal, 1. e.,to the pressure itself.

An output rod is secured to the wall or diaphragm separating the two chambers, and extends outside the apparatus. Suitable resilient biasing means, having the property of increasing the opposing force as the rod is moved from a neutral position, is connected to the rod, so that the output position of the rod becomes a function of boththe rateof change of input pressure and of the input pressure itself, i. e., the fundamental. Since the control fluid in such an apparatus as described above must be compressible, e. g., a gas such as air, it'may be desirable in certain cases to insert a diaphragm between the input conduit and the device itself, so that an incompressiblefluid, e. g., a liquid such as oil, mayTbe used in the input conduit, its pressure being transmitted thru the diaphragm to air, which then flows back and forth between the two opposed chambers.

'The combined, fundamental and rate respon' sive device described'above is conveniently emp'loyed in a push-pullsystem, in which two such benenlarges, the other automatically ensmalls The chambers are so arranged that the pressure sensitive area of the wall facing one chamber is greater than that facing the other, so that for equal'pres'sure areas in both chambers, the forces pther'of the two chambers The by-pass conduit increases, pressure in the other decreases.

devices are placed in opposition, their respective output. rods feeding a common output member, and their input conduits being so controlled in push-pullfashion that as pressure in one device The common output member isso connected tothe twojoutputrods of the opposed devices that an outputmovement in a common sense, or direction, is derived, in typical push-pull fashion.

For amplification of signal power, this common push-pulloutput member is preferably connected to a valve in a hydraulic system, this valve controllingthe application of fluid to a hydraulic servo such as a cylinder and piston.

The hydraulic valve may comprise a pair of cooperating members such as a cylinder and a reciprocatingpiston, one' of the members, for ex ample, thepiston, being reciprocated by the output member from the fundamental-and-rate-responsive devices described above. The valve serves to control admission of oil selectively to either end of a hydraulic servo cylinder, depending on the position'of the valve piston. In cert'ain'caisfes itmay'be desired that the move,

ment of the hydraulic servo be proportional to the integral of the output from the rate responsive devices. In other cases, however, integration is not desired; and to that end it is required that some means be provided for stopping flow of fluid into the hydraulic servo cylinder which the servo piston has'm'oved a distance corresponding to the output signal from the rate responsive devices. To such an end, a feedback link is connected between the hydraulic servo piston and the cylinder or casing of the-valve, causing the casing to move in the same direction as the valve piston, thereby compensating "for the movement of the piston. In thisway, integration of the signal is avoided, and the ultimate output signal at the servo becomes directly "a function of the input signal and the rate of change of the input signal.

Specific embodiments of apparatus constructed in accordancewith the instant invention'will now bedescribed-withreferenoe to the accompanying drawing, wherein:

Fig. 1 represents "schematically a combined fundamental and-rate responsive device forming an-important component of the complete system of the instant invention;

Fig. -2 illustrateshow the device of Fig. 1 may be'modifiedto accommodate it for receiving pressure signals from anincompressible fluid such as oil; and

Fig. 3 illustrates a complete fluid servo system employing both 'air and'oiLto achieve'the-final result of a high power output signal proportional simultaneously to both the fundamental and rate or change of a low power'input signal.

-InFig. 1, ll denotes a housing or'casing to which is connected an input conduit 1 2 adapted to transmit to the 'housing *H a compressible fluid such as air. The pressure of the air represents the input signal whichis to lee-operated on by-the device in such a'fashion that anoutput signal 'isderived proportional simultaneously to both the'fundamental andrate of'change of the air pressure in the input conduit [2. A bellows l 3, closed by a'wall M, and communicating with the input conduit I2,-forms a first expansible chamber tfiwithinthehouslng'l l. The remainder of the housing ll constitutes a second expansible chamber l1, soarrangedthat as the chamber [6 enlarges,'thereby moving the wall M to the right, the chamber I! must automatically become smaller.

'To'de'rive an outputthat is proportional both to the'fundamental and'the rate'of change of the input signal, it is 'necessary'th'at "the pressure effective areas on the two sides of the wall M,

exposed to the chambers 16 andl'Lrespectively,

be different. 'To .that'end, a smallerbellows I8 is mounted to the wall I, and extends thru'the chamber [1 tolthe' wall of the housing H, where it communicates with atmosphere, thereby reducing the area of the wall I4 which is exposed to the chamber l1 and making the pressure-sensitive area on the side of the chamber 16 greater than that facing the chamber l1. 7

An output rod it connected to the outside face of the wall I4 extends thru the interior of the bellows l8, andis resiliently biased to a suitable neutralposition by means of a pair of springs 2 I, compressed between a washer 22 fixed to the rod l9, and a pair offixedly mounted walls 23. Where resilient metal bellows are used at 13 and f8, the springsZ! may be omitted.

is admitted to the expansible chamber 1 1 thru a conduit 24, "extending from the input to match this force. rest at a predetermined position.

"atmospheric air pressure exists in the input conduit l2. This pressure also exists in the two chambers 16 and H, but since the former is active upon-a greater areaof the wall M, the rod 19 is pressed to the right a predetermined amount until the springs 21 are compressed sufficiently The rod I9 thus comes to Now assume that the pressure in the input conduit [2 increases. This increase isimmediately transmitted into the'chamber l6 and causes the wall I l to move to the right. Pressure in the chamber [1, however, does not increase immediately becauseof the restriction 26. As the air flows past the restriction 28 thru. the conduit =24 and into-the chamber 11, pressurein the chamher I? gradually builds up and slowly returns the wall 14 toward 'the left. However, even after pressure has equalized between the chambers :16

and IT, the new increased pressure causes'the-rod to come to rest at a position somewhat to the right of what it was befora'because-of the-differential in wall-effective areas between the chambers "Sand-l1.

The net result'is-that upon increa'se'in pressure, i. e., when-the inputsignal increases,*the rod i9 moves suddenly to the-right, overshootingits final position, and gradually returning to the 'left until it occupies its new, fundamental position. This represents an output'signal which is pr0- portional both to the fundamental of the input signal and also 'tothe rateof change, or first time derivative of the input signal.

Under certain circumstances, it may-bedesirable to transmit the pressure signals to the-device of "Fig. 1 thru an incompressible 'fluid'such *as oil. In-this-ca'se; the modification shownin Fig. 2 maybe employed toadvantage. In this case, the housing 3| 'is divided into three chambers: 32, 33 and, the-first-communicating directly with the inlet conduit -36"and being separated from'the chamber 33-by-a diaphragmtl. In this way the two opposed chambers 33 and maybe filled-with air, or-other-compressible fiuid,'while pressure -may be-applied thereto by 'oiliin'the chamber'32 thru the diaphragm 31. The'chambers 33 and '3'4- are-separated by a'bellows-38, and area-diiferential being achieveda's .inFig. "1 by a smaller-bellows 39.

In the Fig.2 modification'itis convenient to provide the by pass conduit 4| having "the adjustable restriction '42, directly between 'the two chambers 33-and 35.

Operation of the device o'f'FigsZ is the same as that-of Fig. 1 exceptthat'the'input'pressuresignalin the conduit '36'is transmitted by means' of oilpressure against the diaphragm '31, and then againstthe air inthe chambers "33'and 34.

Turningnow to the 'complete system, Fig. '3, a pair-of fundamental and rate responsivedevices, each vsimilarto that illustrated in'Fig. 1', is illustrated at 43and 4'4,respectively. The devicesat'43 andMl are juxtaposed and faced toward eachcthefin'push-puH fashion, so that a "common'output rod 4'6 may "be employed ex tending between the respective movable walls of the devices 43and 44. The rod 46, at its midpointhas a pin 41, extending thru aslot 48 in a lever 49'pivoted at The lever 49. is biased to a suitable neutral position by means of springs 52.

Air supply for the two devices 43 and 44 comes from a conduit 53 which is bifurcated at 54 into two branches 56 and 5?, supplying the two devices d31and 45-, respectively. The two branches 55 and 5'! are broken at 58 and 59, respectively, so that the air must span an open gap to continue its flow intothe two devices 43 and 4t.

Avalve means is pivotally mounted to control flow of fiuid past the breaks 58 and 59 in pushpull fashion. This valve means assumes the form. of an arcuate vane Bl, pivotally mounted iby-mea'ns of an arm 62 to a'shaft 63, disposed on an axis extending thru the bifurcation 54. .As the shaft 63 is caused to oscillate by virtue of an input signal, thevane Bl likewise oscillates in such'a manner that one end of the vane progressively blocks one of the branches 55-51 while simultaneously progressively opening the otherb-r'anch. For example, when the shaft 63 pivots slightly clockwise in Fig. 3 causing the arcuate vane iii to do likewise, a greater portion of thebreak 58 is covered by the vane iii, and a lesser portionof the break 59 is covered by the other end of the vane tl. Thus, an increased amount of air is admitted to the conduit 51, while adecreased amount is admitted to the conduit 56. The output rod 46 thus receives a signal in thesame sense from both the devices 43 and 44; i. e., the pressure changes in the conduits 5t and .5? are both in such direction as to cause the output rod 43 to move to the left in Fig. 3. As shown, the construction of the vane 6! and associated partsis such that the shaft 63 may rotate thru a full 360 degrees if so required. 7

The force or power derivable from such a device as thus far described in Fig. 3'is generally rather low, and it is desirable to amplify this force before it is actually applied to a response member such as a vehicle rudder. To this end, a valve 64 is provided having a cylinder or casing 66 and a piston or valve member 61 reciprocable within the casing 66. The valve member 61 is linked to the arm 49 by means of an arm 68 From a source 69 ofiiuid such as oil under pressure, oil is applied to the interior of the casing 56 by means of an inputconduit H. A pair of output conduits l2 and 73, positioned to selectively-receive oil from the source 69 in accordance with the relative position between the valve member 61 and the casing 66, are connectedto apply oil tothe respective ends of a servo cylinder 14 in which reciprocates :a piston 16, having an output rod or arm 11 extending thru the end wall of the cylinder 14.

In order that the movement of theoutput rod 11' not be the integral of the movement of the valve member 61, it is necessary to cause the casing 66 to move in compensation, so that the actual output of the rod TI will be proportional directly to the fundamental movement of the valve 6?, and not to the integral thereof. To this end, a rod 18 extends from the other end of the piston 16 thru the other wall of the'cylinder i4, and connects by means of a feedback link H! with the valve casing 56.

The operation of the hydraulic portion of the system of Fig. 3 will now be briefly discussed. Under equilibrium conditions, the piston l6 occupies a positioncorresponding directly to that 6 occupied bythe output member.- :or rod 49 'of the signal rate deriving devices-43 and 44.=In this case, the valve member 61 is in such position in the casing 66 that both of the valve. output conduits l2 and 'l3 are blocked, and'there is no flow of oil from the source 69. Suppose now that the member 49 should move to the right in Fig. 3. This causes a corresponding movement of the valve member 61, thereby exposing the-conduit E3 to oil under pressure fromthe source 69, and simultaneously exposes the conduit 72 to the exhaust conduit 8!, by means of which oil is evacuated from the casing 66. Oil under pressure thus flows thru the inlet conduit H,'valv,e casing 63, conduit. li and into the left hand side of the cylinder 14, forcing thepiston 16 tothe right, while oil is evacuated from the right hand side of the, cylinder 14 thru the conduits 12 and 81, Were it not for the feedback link 14. this action would continue-indefinitely,thereby causing the output rod ll to respond as the integral of the movement of the valvemember 61. However, inthe instant invention, as vthepiston; 16 moves to the right, it causes the casing 86 to also move to the right, thru the, linkage l8, 19, thereby gradually covering the openings of the conduits 12 and 13 which were exposed by the movement of the valve member 61, until these conduits are finally closed. completely. The piston 16 is thus caused to assume a new position corresponding directly to the new position of the out 'putr-od49. I Were the rod 49 to move to the left, a conversev operation would take place, with oil being suppliedto the cylinder 14 thru the conduit '62, and being evacuated thru the conduit Wand the exhaust conduits 82 inthe valve casing 66.

It is to be understood that the operative connections to the two members 66 and 6.1 of the valve 64 may be reversed if desired. That is to say, the input linkage ,68 may be connected to the valve casing 66 instead of to the valve member 61, and the feedback link 19 connected to the valve member 51 instead of to the casing 66. The essential operation of the valve 66' willstill be substantially unchanged. v

In a system as described in connectionwith Fig. 3, it often occurs that undesirable" magnification of high frequency rate response signals occurs in'the devices43 and 4%, so that the high frequency components in the oscillation of the rod t9 are disproportionately large. It is, therefore, desirable that some means be attained for discriminating selectively against high frequency components while allowing the lowerirequency oscillations to come thru unattenuated. This is effected in accordance with the instant invention by inserting somewhere in the oil conduit system feeding the cylinder, a suitable throttle valve, by means of which the rate of flow of oil from the source 69'may be limited. This may be done in either of the conduits ll, 12 or E3 or in more than one of these conduits. In the example shown in Fig. 3, this throttle valveis shown at 83 interposed in the inlet'conduit HQ l The action of the valve 83 is'substantially as follows: assume that a high frequency signal is obtained on the output rod 49 so-that it moves rapidly to the right. This exposes the port feeding the conduit 13, so that the piston H5 starts to move to the right. However, by virtue of throttling action of the valve 83, oil can :enter the left hand side of the cylinder 14 at only a predetermined rate, so that. therate of movement of the piston 16110 the rightis thereby limited to a accuse:

predetermined maximum.- Before the piston 16 has an opportunity to move to the full excursion demanded of it by the rapid signal from the rod 49, the latter returns to the left by virtue of the short periodicity (high frequency) of the signal under consideration, thereby closing the conduit 13; and, if the excursion is large enough, exposing the conduit 12 to the action of the high pressure oil from the source 69. It will thus be seen that for such a rapid oscillation of the output rod 49, the piston 16 is unable 'to follow as rapidly as demanded of it by the rod 49. In this way, high frequency signals appearing on the rod 49 are attenuated directly in proportion to the frequency, the lower limit frequency of this attenuation "being determined by the setting of the valve 83.

No attenuation is experienced for low frequency signals; because as the valve 61 moves slowly to theright (or left, as the case may be), the opening exposed to the conduit 13 is rather small, and it is this opening rather than the re striction of the valve 83 which is the controlling factor in determining the speed of movement of the piston 16. Thus, for low frequencies the piss ton 16 isable to follow faithfully the movement of the rod 49,. and the valve 83 has not restrictive effect.

Operation For a comprehensive understanding of the over-all operation of the system disclosed in Fig. 3, a complete cycle of operation will now be described. Under a steady state condition, air flows steadily thru the conduit 53 into the two branches B and 51, past the breaks 58 and 59, and enters the two rate responsive devices 43 and 44. The pressure in these two devices will thus be of such magnitude that the output rod 49 assumes a defiinite position, depending directly upon the position of the input signal vane 65. Likewise, the valve member 61 and the piston 16 assume positions corresponding directly to that of the rod 49, and thus of the input vane 6|. We thus find the ultimate output rod 11 residing at a position which is a unique, single valued function of the position of the vane 6|.

Assume now that a signal from the shaft 63 causes the arcuate vane 6| to pivot clockwise. This exposes more of the gap 59 and less of the gap 58 to the air stream from the conduit 53. Pressure is thus increased in the device 44, and decreased in the device 43. The output rod 46 moves to the left, overshooting its final value, and then returning to the right where it finally comes to rest at a position corresponding directly to the position of the shaft 63. The overshooting is due to the rate responsive nature of the devices 43 and 44,. as described hereinbefore in connection with the description of Fig. 1. The net result is that the output rod 49 in Fig. 3 moves in accordance with a signal which is directly proportional to both the fundamental and first time derivatives of the signal applied thru the shaft 63. When theshaft 63 has stopped moving for an appreciable time so that steady state conditions are again imposed, the output rod 49 will have assumed a steady statecondition directly proportional to the new position of the shaft 63.

Whatever the movement of the rod49 is, it will be followed directly by the valve member 6-! thru the arm- 68. Whenthe. rod 49 moves to the left, the piston 61 likewise moves to the left, exposing the conduit 12 to the highqpressure oil from the source 6.9, forcing the-piston 16 to the left'until thecasingxtli .istcompensatorily moved :thru the linkage 19 a distance sufficient to close the'po'rt feeding the conduit 12, whereupon motion of the piston it stops at its new position corresponding to that of the valve member 61. The piston 16 follows faithfully the movement of the rod 49 including the rate responsive overshoot, except that when the overshoot occurs atahigh frequency beyond the limiting capacity of the throttle valve 83, then such high frequency is attenuated, and the full swing of the rod 49 is not obtained in the piston 16.

The net result is as follows: The output member 71, secured to the piston 16, follows the input signal and the rate of change of the input signal applied to the vane 6| faithfully, except that high frequency components in the movement of the rod 49, introduced usually thru the rate responsive devices 43 and 44, are not followed faithfully, but are attenuated, by the piston 16, the attenuation increasing with increasing frequency.

It is to be understood that either'of the rate responsive devices shown in Fig. l or 2 maybe substituted for the double bellows arrangement 43-44 incorporated in Fig. 3. In such case the signal may come from any device capable of delivering a pneumatic pressure proportional to the signal to be amplified.

Alternatively the variable pneumatic pressure may be achieved by using half of the vane 6| to regulate a single conduitsupplying either of the devices in Fig. 1 or 2.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

The invention described herein maybe manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A pressure sensitive control device comprising: a pair of chambers, a diaphragm for each chamber dividing the same into two compartments, the pressure sensitive area on one side of diaphragm being greater than on the other, and a restriction connecting the compartments; a source of fiuid under pressure; two conduits respectively connecting 'said source to a compartment of each chamber; valve means operable to increasingly restrict flow thru one of-said conduits while permitting increased flow thru the other; and an output member connected in'pushpull relation to both diaphragms.

2. A pressure sensitive control device comprising a pair of chambers each having a movable wall dividing the chamber into two compartments with a greater pressure sensitive area on one face of the wall than on the other, an adjustable orifice in each said Wall connecting its two compartments, a source of fluid pressure, two conduits connecting said source respectively to one compartment of each chamber, valve means operable to increasingly restrict flow thru one of said conduits while deereasingly restricting flow thru the other of said conduits, a movable output member, and a common actuating member connecting both. said walls to said output member in push-pull relation.

HORACE E. KARIG.

(References on following page) References Cited in the file 6! this patent UNITED STATES PATENTS Number Name Date Moller Oct. 30, 1934 5 Moller Sept. 6, 1938 Berger Feb. 21, 1939 Bannon .1 Apr. 18, 1939 Schweizer Oct. 31, 1939 Number 10 Name Date Rebeski Nov. 12, 1940 Halford Mar. 21, 1944 Shoults May 1, 1945 Larson June 26, 1945 Lee Nov. 9, 1948 Hermanny July 12, 1949 Moore July 25, 1950 

